Small fruit need a certain period of time under 45F, this period is known as the chilling requirement. Different small fruit, and even different varieties, have different chilling requirements. For example, raspberries have rather high chilling requirements, between 800 and 1,800 hours, while blackberries have a low chilling requirement, between 200-900 hours. Chilling requirements of blueberry vary widely between types, i.e. northern highbush (approx. 800-1,000), southern highbush (approx. 150-800) or rabbiteye (approx. 300-600).
The blackberry variety Oachita, popular WNC, is thought to have a mid-chilling requirement of 400 hours. Navaho, another widely produced variety for our region, has a 800-900 chilling hour requirement. Tupy, the primary blackberry grown in Mexico, has a chilling requirement of 200 hours.
Because of the mild winter thus far in the Southeast, there is concern that the small fruits will not accumulate the chilling hours necessary for proper production.
Dr. Gina Fernandez, small fruit specialist at NC State, shared a link to a new tool offered by the NC Climate Office in collaboration with small fruits specialists. This tool offers data that shows the chilling units accumulated in different weather stations across the southeast for blueberries, blackberries and strawberries.
You can find the data here: http://www.nc-climate.ncsu.edu/products/ag/berries
For the Fletcher weather station, it appears that we are at almost 600 chilling hours for blackberry and 1210 for blueberry, therefore well on our way to meeting our chilling requirements this season.
To keep up with the latest from Dr. Fernandez and Team Rubus, check out the below social media and sites.
Web Portal: http://ncsu.edu/enterprises/blackberries-raspberries